Inkless fingerprint scanners, also known as live scan fingerprint readers or biometric devices, have been widely used for many years. These systems obtain an image of the fingerprint without the use of inks. Once an image is acquired, it is then processed and an identification or verification of the individual's identity is made.
Many different techniques have been used to obtain an image of the finger including optical scanners, thermal scanners, capacitive scanners, E-field sensors, ultrasonic scanners, and many more. Each uses a different modality or technique to image the same physical characteristic; the ridge structure of the finger. Each claim to have certain advantages over the competing approaches.
The use of these systems is a two step process. The first step is that the user must enroll into the system. The enrollment process scans the individual's finger for the first time and stores it, along with any other pertinent information needed for future use in the identification or verification process. The second step is the actual identification or verification process. In the case of identification, the user's identity is now known and it is up to the system to determine the identity. This process is usually referred to as a cold search or a one-to-many. The verification process is where the user presents their identity in the form of a token such as a PIN code, ID Card, etc., and it is up to the system to verify the identity using the fingerprint.
The majority of large-scale applications that have been attempted with live scan fingerprint readers have been in an attended application. That is, a trained attendant assists the user of the live scan fingerprint reader by guiding the user in the proper placement of the finger with respect to vertical and horizontal position on the platen surface of the live scan fingerprint reader. Proper placement of the finger is absolutely critical to obtain maximum accuracy in the identification or verification process. Usually, a display such as a computer monitor is used to show the location of the finger on the platen, providing feedback to the user and the attendant as to the position of the finger. In addition to proper placement of the finger horizontally and vertically, users often tend to roll the finger to one side or another, thereby not imaging the main portion of the finger but rather the side of the finger. Consequently, the attendant will often assist in ensuring that the finger is flat on the fingerprint platen and not rolled off to one side.
Using an attendant to assist the user and providing visual feedback of the image severely limits the deployment of these systems. For example, for most commercial applications the cost of a trained fingerprint attendant to assist the user in the positioning of their finger is prohibitive. Techniques to train the users on the proper placement of the finger have been tried but generally do not work. Even if they did, adding a PC Monitor near the fingerprint scanner to provide positional feedback also raises the cost of the system beyond what can be tolerated by most commercial applications. Furthermore, the visual feedback system introduces additional problems.
First, the user, by seeing the finger on the PC Monitor, will tend to slide their finger into position until it is properly located. Because of the friction between the skin and the platen, the sliding effect introduces distortion of the fingerprint, thereby introducing errors in the identification/verification process.
Second, many live-scan fingerprint readers cannot produce an image of the finger fast enough to give the user the instantaneous feedback they need to guide them. For these scanners, the use of a display such as a PC Monitor is virtually useless.
In an attempt to solve this problem, some of these products have tried a form of electrical or mechanical guide to assist the user in the proper placement of the finger. Electrical guides are normally some type of sensor or array of sensors that is detecting the position of the finger on the platen surface and providing the user feedback. Again, these devices would have the same problem associated with them as does the PC Monitor. The user would slide their finger to position it properly as instructed by the positioning sensor, and this sliding would again cause distortion of the fingerprint. Other electronic means have been proposed to image a very large surface area, thereby ensuring that the entire finger would be imaged. Then using image-processing techniques, the tip of the finger would be located for processing the fingerprint image. Unfortunately, for many fingerprint scanners, imaging a large scan area would cause the image array such as a CCD to increase in size, thereby increasing the cost of the system significantly. For other fingerprint scanners, increasing the image area would increase the scan time significantly thereby reducing user acceptance and system throughout.
Stationary mechanical devices have been tried but have proven ineffective. The variability in the length, width and height of fingers makes it difficult to design a single guide to work for everyone. In addition, many proposed techniques have proven inappropriate due to the variability in the length of an individual's fingernails.
These problems combined have restricted the deployment of live scan fingerprint readers successfully into unattended applications.